1. Field of the Invention
The invention relates to a honeycomb body having an axis and having a jacket tube into which a configuration including at least one stack wound about the axis in the form of an involute is fitted, the stack having a plurality of metal sheets layered one on the other, and the plurality of sheets including a plurality of structured sheets.
The invention relates in particular to honeycomb bodies for use as carriers of a catalyst for effecting a catalytic reaction in a fluid flowing through the honeycomb body. Such use is made particularly in the exhaust system of an internal combustion engine which, for instance, drives a motor vehicle, in which the fluid is an engine exhaust gas in which reactions are to be effected by the catalyst in order to convert pollutants into unobjectionable substances.
A metal honeycomb body that is suitable as a catalyst carrier body and has layers being extended in involute fashion and being formed of smooth and corrugated sheets, is described in Published European Application No. EP 0 245 736 B1. A further development is found in Published European Application No. EP 0 245 737 B1, corresponding to U.S. Pat. Nos. 4,923,109 and 4,832,998. That disclosure describes forming the honeycomb body by wrapping the ends of a stack that is formed of smooth and corrugated sheets layered on one another, in an S shape about an axis, by means of which two approximately involute structures that are wound around one another are produced. Another feature of the honeycomb body with layers aligned in involute fashion is found in Published International Application WO 90/03220, corresponding to U.S. Pat. No. 5,135,794. In that disclosure, stacks of metal sheets, some of which are structured and which are folded at a bending line are wound around one another and around an axis aligned parallel to the bending lines. The honeycomb bodies described in those three references are usable in particular as carriers for catalysts in motor vehicle exhaust systems and further details may be found in those references.
In order to reach a sufficient efficiency of the catalysts on honeycomb bodies in exhaust systems of motor vehicles, honeycomb bodies having cross sections which are equal the cross sections of the exhaust gas pipes, through which the exhaust gases flow from the internal combustion engines to the honeycomb bodies or away form the honeycomb bodies, are usually not sufficient. Accordingly, diffusers have to be provided in front of honeycomb bodies and confusers behind honeycomb bodies in exhaust gas systems of motor vehicles, in order to adjust the cross sections of exhaust gas pipes and honeycomb bodies to each other. Details thereof are found in Published European Application EP 0 386 013 B1, corresponding to U.S. Pat. No. 5,150,573. That reference also gives a detailed explanation of the problems of a steady inflow of a honeycomb body carrying a catalyst. In order to improve the inflow, a flow guide body with a shape adapted to the shape of the diffuser or confuser, which means a conical shape, should be inserted in the diffuser in front of and/or in the confuser behind a honeycomb body. Such a flow guide body may possibly be a honeycomb body itself and can, for example, be formed of spiral windings of a corrugated and slit metal sheet. Other possibilities for forming the conical honeycomb body amount to an assembly of numerous homogeneous, conical, pipe-shaped elements. The conical honeycomb body which mainly serves as a flow guide body can additionally receive a catalytically effective coating itself, in order to serve as a "precatalyst" , besides the cylindrical honeycomb body having a catalyst which is still supposed to carry the main load of the catalytic conversion. Since the flow guide body usually contains considerably less mass than the cylindrical honeycomb body, it heats up faster at start-up and a catalyst located on it can become effective during an especially short period of time.
According to German Patent DE 23 13 040 C3, corresponding to U.S. Pat. No. 3,907,708, a slightly conical honeycomb body can be built by pressing a cylindrical structure, which forms a layer of flat and corrugated metal sheets.
Published International Application WO 90/08249, corresponding to U.S. Pat. No. 5,157,010; Published European Application EP 0 298 943 A2; Published International Application WO 91/01178, corresponding to co-pending U.S. application Ser. No. 711,564, filed May 30, 1991 and application Ser. No. 900,836, filed Jun. 18, 1992; Published International Application WO 91/01807, corresponding generally to U.S. Pat. Nos. 5,045,403 and 5,130,208; and Published European Application EP 0 136 515 B1, relate to the formation of microstructures in metal sheets from which honeycomb bodies are intended to be formed. Examples of such microstructures are flutes, beads, bumps, grooves, or small pieces of the surface protruding from the metal sheets. They are generally markedly smaller than the corrugations that are understood in professional circles to be made in "corrugated" sheets for producing honeycomb bodies. The microstructures serve various purposes. They can contribute to improving the strength of a honeycomb body, if the body is constructed in such a way that the microstructures intermesh. The microstructures may also serve, optionally in addition to that function, to influence the flow behavior of a fluid passing through a honeycomb body.
German Published, Non-Prosecuted Application DE 39 03 879 A1 discloses a metal honeycomb body which is disposed in the closed gas loop of a laser, is intended to trip certain catalytic reactions in the gas required for operating the laser and is electrically heatable.
Electrically heatable honeycomb bodies are also usable in motor vehicle exhaust systems. That can be learned, for instance, from Published International Application WO 90/12951, which moreover describes a further function of microstructures in metal sheets from which an electrically heatable honeycomb body is made. The microstructures serve the purpose of providing a form-locking connection of two metal sheets, between which an electrically insulating intermediate layer of ceramic or the like is inserted. A form-locking connection is one which connects two elements together due to the shape of the elements themselves, as opposed to a force-locking connection, which locks the elements together by force external to the elements. German Published, Non-Prosecuted Application DE 37 19 773 A1 discloses a carrier body for a catalytic reactor for exhaust gas cleaning, which is conical in structure and is associated with a likewise conical jacket tube.